DESCRIPTION (Applicant's Abstract): The proposed studies will address the issue of selective vulnerability of neurons in Alzheimer's disease. Underlying these studies is the hypothesis that excitotoxicity, particularly that which is mediated via stimulation of ionotropic glutamate receptors, contributes to the neuro-degeneration of Alzheimer's disease. Moreover, we predict that in Alzheimer's disease the perturbation of specific glutamate receptor subunits, particularly those involved in the gating of calcium, may contribute significantly to the viability of the cell. The current investigation focuses on the N-methyl- D-aspartate (NMDA) receptor. Notably, previous work of ours has focused on the distribution and expression of specific non-NMDA (i.e. AMPA) receptor subunits in the hippocampus of patients with Alzheimer's disease pathology. Collectively, these investigations attempt to provide a comprehensive understanding of the anatomy of the ionotropic glutamate receptor in the hippocampus of normal subjects and in subjects with Alzheimer's disease. In this application, we propose a series of highly correlated immunohistochemical (Specific Aims 1&2), biochemical (Specific Aim 3) and in situ hybridization studies investigating the distribution and level of expression of specific NMDA receptor subunits (e.g., NMDAR1, NR2A, NR2B, & NR2D). Studies will focus on the human hippocampus, in part, because this region is known to be affected very early within the progression of the disease. Subjects representing a broad range of neuropathologic severity (i.e. Braak stages I-VI) will be studied thus providing us with the opportunity of examining alterations in glutamate receptor expression throughout various stages of the disease. Moreover, the use of specific antibodies identifying early events in the evolution of neurofibrillary pathology provides an additional opportunity of correlating alterations in NMDA receptor subunit expression with initiating events of neurodegeneration. An understanding of the anatomical organization of NMDA and AMPA receptors and the mechanism underlying glutamate-mediated excitotoxicity is important before appropriate drugs aimed at halting Alzheimer's disease-associated neuronal degeneration can be developed.